252 WEED FLORA OF IOWA 



if dodder reseeds itself its control becomes much more difficult or 

 impossible. This is the prevailing condition in the west. The fact 

 that the small-seeded alfalfa dodder of the west has not become 

 established in the east is of special interest in this connection. 

 Clover dodder appears likely to prove the most troublesome in 

 alfalfa culture in the east. 



"If the dodder occurs only in patches in the field it usually can 

 be controlled by hand methods. If it covers the greater part or all 

 of the field, plowing under the stand will probably be found nec- 

 essary. It then becomes important to know how far the crop can 

 be utilized without reseeding the land to dodder." 



Field Dodder (Cuscuta arvensis Beyrich.). 



Description. — Stems pale and slender, filiform ; flowers rather 

 small, in sessile clusters; calyx with 5 obtuse broad lobes; corolla 

 with a short, wide tube, innexed points, 5-lobed, acute or acumi- 

 nate, about y 2 as long as the tube, tips reflexed; scales large and 

 deeply fringed; stigmas capitate; capsules globose, indehiscent. 

 Occurs on shrubs, clover and other herbs. 



Distribution. — Massachusetts to Wisconsin and westward. In- 

 troduced with clover and alfalfa seed in Iowa. 



Extermination. — The dodders are largely spread through com- 

 mercial seeds, like flax, clover and alfalfa. Alfalfa dodder is a 

 somewhat troublesome Aveed in sections of the United States and 

 Europe where alfalfa is grown ; in this way it has made its way 

 into the Mississippi valley in recent years. There has been much 

 complaint about the appearance of clover and field dodder in the 

 same region, largely spread, of course, through commercial seeds. 

 The dodder may be exterminated in the following way: 



First by the herbicidal treatment, For this purpose a liberal 

 application of a 10 per cent solution of copper sulphate will be 

 found efficacious. 



In addition, the European investigators recommend a strong sol- 

 ution of salt, sulphide of lime, carbolic acid, and sulphate of iron. 

 These solutions will destroy the dodder when found in the vegeta- 

 tive condition, but should seed occur, then it will be necessary to 

 take the additional precaution of cutting the dodder after the ap- 

 plication of the herbicide and burning it, It should be remembered 

 that these solutions will not be effective unless they come in direct 

 contact with the plant. They will injure the clover plant as well. 



